To have an unpleasant interaction with someone. I'm not going to her party because my ex-boyfriend will be there, and I don't want to have a run-in with him.
have a ˈrun-in with somebody
(informal) have an argument or disagreement with somebody: She had a run-in with her son’s teacher this morning. She doesn’t think he gives the children enough homework.
have a run-in (with someone/something)
tv. to have trouble with someone or something. I had a run-in with Mrs. Wilson. She’s a hard case.